This disclosure relates to converting the hydraulic power of drilling fluid moving through a drill string into a stable supply of electrical power, despite changes in drilling fluid flow rate.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A drill bit attached to a long string of drill pipe, generally referred to as the drill string, may be used to drill a borehole for an oil and/or gas well. In addition to the drill bit, the drill string may also include a variety of downhole tools to measure or log properties of the surrounding rock formation or the conditions in the borehole. These tools often require power to operate. To generate this power, a turbine generator may convert hydraulic power of drilling fluid moving through the drill string.
Specifically, in the drilling process, drilling fluid is pumped down into the drill string to mechanically power the rotation of the drill bit and to help remove rock cuttings out of the borehole. The drilling fluid may pass over one or more turbines of a turbine generator to transform hydraulic power into rotational mechanical power. The rotational mechanical power may be transformed by an alternator into electrical power.
While the amount of electrical power provided by the turbine generator generally depends on the flow rate of the drilling fluid, the electrically powered tools of the drill string may operate within a range of possible input voltages and currents. Various systems have been developed to maintain the reliability of these electronic components as the flow rate of the drilling fluid changes. These systems, however, have many disadvantages. For example, a gearbox may transform the input rotation speed of a rotating shaft into a higher or lower rotation speed to enter the alternator of the turbine generator. Still, such a gearbox may require substantial maintenance and may increase the complexity of the downhole turbine generator system. Likewise, a fluid braking mechanism that is external to the turbine generator also has been developed. Such an external fluid braking mechanism may effectively prevent some excessive rotation speeds of the rotating shaft of the turbine generator. The external fluid braking mechanism may be dependent on characteristics of the drilling fluid, however, which may vary from drilling operation to drilling operation.